Effect of crosslink density on thermal conductivity of epoxy/carbon nanotube nanocomposites

The effect of the polymeric crosslink density on the thermal conductivity of an epoxy nanocomposite was investigated by adding two different diamine-functionalized multiwalled carbon nanotubes (diamine-MWNTs) to the epoxy resin as co-curing agents and conducting fillers. Tetramethylenediamine (TMDA)-MWNTs resulted in an epoxy nanocomposite with a higher crosslink density than octamethylenediamine (OMDA)-MWNTs. Interestingly, epoxy/TMDA-MWNT nanocomposites under 1.5 wt % nanotube concentration, showed a higher thermal conductivity than an epoxy/OMDA-MWNT nanocomposite with the same concentration of nanotubes. In contrast, for higher diamine-MWNT concentrations (over 2.0 wt %), the thermal conductivity of the epoxy/OMDA-MWNT nanocomposite was higher than that with TMDA-MWNTs. We observed that for low MWNT concentrations, where a percolating network was not formed, a high crosslink density enhanced the thermal conductivity via phonon transport. However, for high MWNT concentrations, a high crosslink density hinders the formation of a percolating network and lowers the thermal conductivity. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44253.